1. Technical Field
The present invention relates to an optical modulator, and in particular, to an optical modulator module package.
2. Description of the Related Art
An optical modulator is a circuit or device which loads signals on a beam of light (optical modulation) when the transmission medium is optical fiber or free space in the optical frequency range. The optical modulator is used in such fields as optical memory, optical display, printers, optical interconnection, and holograms, etc., and a great deal of development research is currently under way on display devices using the optical modulator.
The optical modulator may involve MEMS (Micro Electro Mechanical System) technology, in which three-dimensional structures are formed on silicon substrates using semiconductor manufacturing technology. There are a variety of applications in which MEMS is used, examples of which include various sensors for vehicles, inkjet printer heads, HDD magnetic heads, and portable telecommunication devices, in which the trend is towards smaller devices capable of more functionalities.
The MEMS element has a movable part spaced from the substrate to perform mechanical movement. MEMS can also be called a micro electromechanical system or element, and one of its applications is in the field of optical science. Using micromachining technology, optical components smaller than 1 mm may be fabricated, by which micro optical systems may be implemented. Specially fabricated semiconductor lasers may be attached to supports prefabricated by micromachining technology, so that micro Fresnel lenses, beam splitters, and 45° reflective mirrors may be fabricated and assembled by micromachining technology. Existing optical systems are composed using assembly tools to place mirrors and lenses, etc., on large, heavy optical benches. The size of the lasers is also large. To obtain performance in optical systems thus composed, significant effort is required in several stages of careful adjustment to calibrate the light axes, reflective angles, and reflective surfaces, etc.
Micro optical systems are currently selected and applied in telecommunication devices and information display and recording devices, due to such advantages as quick response time, low level of loss, and convenience in layering and digitalizing. For example, micro optical components such as micro mirrors, micro lenses, and optical fiber supports may be applied to data storage recording devices, large image display devices, optical communication elements, and adaptive optics.
For these functions, micro mirrors are applied in various ways according to the direction, such as the vertical, rotational, and sliding directions, and to the static and dynamic movement. Movement in the vertical direction is used in such applications as phase compensators and diffractometers, with movement in the direction of inclination used in applications such as scanners or switches, optical splitters, optical attenuators, and movement in the sliding direction used in optical shields or switches, and optical splitters.
The size of a micro mirror is 10 to 1000 μm, and the number of mirrors fabricated for an application is about 1 to 106. While the size of a micro mirror in a large screen display device is small, being about 10 to 50 μm, a number of mirrors corresponding to the number of pixels are required, so that about one million mirrors are needed. In the case of adaptive optics or in optical splitters, the size of a mirror is somewhat larger, being 10 to 50 μm, but the required number is smaller, being about several hundred. In the case of scanners or optical pick-up devices, the mirrors are increased to about several mm, where just one mirror may be sufficient for application. Thus, the size and number of micro mirrors vary considerably according to the application, and the application varies according to the direction of movement and to whether the movement is static or dynamic. Of course, the method of fabricating the micro mirrors also varies accordingly. While the mirrors in a large screen display device have sizes of several tens of μm, their response times are quite speedy, being about several tens of μs, whereas the mirrors in an optical splitter have sizes of several hundred μm and response times of several hundred μs. Mirrors having sizes of several mm are used in scanners, etc., and have response times of several μs.
FIG. 1 is an exploded perspective view of a conventional optical modulator module package. As seen in FIG. 1, the optical modulator module package 100 includes a substrate 110, a transparent substrate 120, an optical modulator element 130, driver integrated circuits 140a to 140d, a heat dissipation plate 150, and a connector 160. Here, the transparent substrate 120 is such that allows the formation of fine-pitch wiring and bump arrays, so that not only a printed circuit board, but also a glass substrate, silicone substrate, LTCC substrate, or multi-layer PCB may be used.
The substrate 110 is a typical semiconductor substrate, and the lower surface of the transparent substrate 120 is attached onto the substrate 110. Also, the optical modulator element 130 is attached to the upper surface of the transparent substrate 120 in correspondence to the hole formed on the substrate 110.
The optical modulator element 130 modulates the incident light inputted through the hole of the substrate 110 and emits diffracted light. The optical modulator element 130 is flip chip connected to the transparent substrate 120. Adhesive is placed around the optical modulator element 130 to form a seal from the outside environment, while electrical connection is maintained by the electrical wiring formed along the surface of the transparent substrate 120.
The driver integrated circuits 140a to 140d are flip chip connected around the optical modulator element 130 onto which the transparent substrate 120 is attached and supply driving power to the optical modulator element 130 according to control signals inputted from the outside.
The heat dissipation plate 150 removes heat generated from the optical modulator element 130 and the driver integrated circuits 140a to 140d, and thus a metallic material is used which readily dissipates heat.
A method of manufacturing the optical modulator module package 100 illustrated in FIG. 1 includes: attaching the connector 160 to the substrate 110, attaching the optical modulator element 130 and driver integrated circuits 140a to 140d to the transparent substrate 120; providing the heat dissipation plate 150, stacking the transparent substrate 120 on the substrate 110 and performing wire bonding, attaching the heat dissipation plate 150 to the optical modulator element 130 and the driver integrated circuits 140a to 140d, and mounting the optical modulator element 130 and the driver integrated circuits 140a to 140d to form an optical modulator module package 100.
It is to be noted that the optical modulator module package 100 illustrated in FIG. 1 has a relatively large number of components, and since each of the numerous components require a suitable amount of space for mounting, there is a limit to how much the size of the module package can be minimized. Also, in mounting the optical modulator element 130 directly on the transparent substrate 120, the electrical/optical functions are concentrated on the transparent substrate 120, whereby the costs for fabricating the necessary transparent substrate 120 is increased. Further, as the optical modulator element 130 is mounted directly on the transparent substrate 120, the narrow gap between the optical modulator element 130 and the transparent substrate 120 increases the influence of foreign substances. Other problems may also occur during the process of mounting the optical modulator element 130 directly on the transparent substrate 120, such as contamination and scratching due to foreign substances.